JPH09180709A - Manufacture of positive electrode mix for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To a provide a positive electrode mix at a small grain diameter, in which unevenness of the grain diameter is restricted and which can be accurately measured, by extruding the wet mixture, which contains the positive electrode active material binder and the conductive material, for granulation, and reshaping the granulated material in a rotary disc. SOLUTION: The positive electrode active material, the conductive material and the binder mixed with the eater. This mixture is put into an inline screw granulator from a hopper 5, rotating a screw 2. The mixture 4 is kneaded in a cylinder 6, and while extruded, and discharged from a through hole 7. The mixture 4 is sheared at the time of passing through an extruding blade 3 fixed to the tip of the extruding screw 2, and after discharged from a semi- spherical dies 1, shared by the self weight so as to obtain the cylindrical granulated material. This granulated material 8 is put onto the rotary disc. The cylindrical granulated material 8 is rotated by the centrifugal force due to the rotation of the rotary disc 12 and the blown-up air so as to be reshaped into the spherical shape. This reshaped product is dried by the hot air so as to obtain the positive electrode mix.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a granular positive electrode mixture used in a battery.

[0002]

2. Description of the Related Art Heretofore, a granular positive electrode mixture has been produced by stirring and granulating a mixture of an active material, a binder and a conductive material in a predetermined mixing ratio by shearing and kneading with a stirring blade. After drying this granular positive electrode mixture, it is filled in a cell of a predetermined volume and the partition rod is moved along the upper edge of the cell to smooth the upper surface of the filled positive electrode mixture and to remove excess positive electrode. Weighing was performed by slicing to remove the mixture. After that, pressure molding was performed to produce a pellet-shaped positive electrode. In recent years, the use of batteries for small devices such as electronic desk calculators and wristwatches has increased, and there has been a demand for smaller and thinner batteries. Therefore, the amount of the positive electrode mixture used per battery is extremely small, and it is necessary to reduce the variation in the weight of the positive electrode. Further, there has been a demand for a positive electrode mixture having high reaction efficiency and excellent discharge characteristics even under heavy load.

[0003]

To meet these demands, a granulated product of a positive electrode mixture having a particle size of 40 to 500 μm and a large specific surface area by increasing the porosity is required. . However, since the positive electrode mixture obtained by the above-described stirring granulation has a large particle size and a large variation, the weight variation is large when the positive electrode mixture is weighed by slicing. Further, the granulated product had a small porosity. An object of the present invention is to provide a positive electrode mixture which has a small particle size and a small variation in the positive electrode mixture and can be accurately measured even by slicing. Further, the present invention has a large porosity,
An object of the present invention is to provide a positive electrode mixture having excellent discharge characteristics even under heavy load.

[0004]

A method for producing a positive electrode mixture for a battery according to the present invention has a wet mixture containing a positive electrode active material, a binder and a conductive material, and has a large number of circular through holes at its tip. A step of producing a granulated product of the mixture by pushing into a screw in-line granulator having an extrusion screw arranged in a cylinder provided with a hemispherical die, and extruding from the through hole by rotation of the extrusion screw, Grain sizing equipped with a hermetically sealed cylindrical container and a rotating disk having a frame-shaped side wall that is horizontally arranged in the cylindrical container and protruding upward, and a mechanism for blowing air from a gap between the cylindrical container and the rotating disk. The method includes a step of forming the granulated product into a spherical shape by charging the granulated product on the rotating rotating disk using a vessel. The diameter of the through hole of the hemispherical die is preferably 0.3 mm or less. Furthermore, the positive electrode active material is a metal oxide, a sulfide,
It is preferably at least one selected from the group consisting of halides and carbon halides.

[0005]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a screw in-line type granulator. The cylinder 6 has a hopper 5 for feeding material in the rear part, and a hemispherical die 1 made of stainless steel having a plurality of circular through holes 7 is fixed to the tip part. The diameter of the through hole 7 is 0.3 mm. The extrusion screw-2 arranged inside the cylinder 6 is rotated in an arrow direction at an arbitrary speed by a motor (not shown) connected to the rear portion. An extrusion blade 3 is fixed to the tip of the extrusion screw 2.

Manganese dioxide as a positive electrode active material, expanded graphite as a conductive material, and fluororesin as a binder are mixed with water in a Henschel mixer, for example. Then, while rotating the extrusion screw 2, the above mixture 4 is charged from the hopper 5. The mixture 4 is extruded in the arrow direction while being kneaded in the cylinder 6 and discharged from the through hole 7. The mixture 4 is sheared when passing through the extrusion blade 3 fixed to the tip of the extrusion screw 2,
Further, since it is discharged from the hemispherical die 1 and cut by its own weight, a columnar granulated material 8 having a length within a predetermined range can be obtained.

2 and 3 show a particle sizer. A rotary disk 12 having a side wall is arranged in the cylindrical container 11, and the granules 8 are formed on the rotary disk 12 from the hopper 10.
Is input. The rotating disk 12 has a bottom portion connected to the rotating shaft 13, and is rotated by a motor (not shown) connected to the rotating shaft 13. Further, air is jetted from the air jet port 14 to the air chamber 15. The sized product 17 sized on the rotating disk 12 is taken out from the discharge damper 16.

As shown in FIG. 3, the columnar granulated material 8 charged into the granulator from the hopper 10 falls on the rotating disk 12 which is rotating horizontally. The dropped cylindrical granules 8 are
Due to the centrifugal force due to the rotation of the rotating disk 12 and the air blown up from the gap between the outer peripheral portion of the rotating disk 12 and the cylindrical container 11, the donut-shaped rotating motion is performed along the side wall of the cylindrical container 11 like a rope. . By this movement, the cylindrical granulated product 8 is sized to be spherical. Rotating disk 12 and cylindrical container 11
The air blown up from the gap of (1) serves both to prevent the cylindrical granulated material 8 from leaking and to prevent it from adhering to the rotary shaft 13. The columnar granulated product 8 is taken out from the discharge damper 16 which is opened as a sized product 17 by rotating at least half a turn on the rotary disc 12. The sized product thus obtained is dried with hot air to obtain a positive electrode mixture.

[0009]

Next, specific examples of the present invention will be described. 5 kg of manganese dioxide as a positive electrode active material, 300 g of expanded graphite as a conductive material, and polytetrafluoroethylene-hexafluoropropylene copolymer 5 as a binder.
0 g and 1 kg of water were mixed in a Henschel mixer for 2 minutes. Here, the expanded graphite is obtained by inserting sulfuric acid between the layers of the flake graphite to expand the layers and then removing the sulfuric acid by washing to increase the specific surface area. While rotating the extrusion screw 2 at 30 rpm, the mixture 4 obtained as described above was charged from the hopper 5 to obtain a columnar granulated product 8. The columnar granulated product 8 obtained as described above was put into a sizing device, and the sized product 17 taken out from the discharge damper 16 was dried with hot air at 150 ° C. to obtain a positive electrode mixture.

[Comparative Example] As a comparative example, 5 kg of manganese dioxide as a positive electrode active material, 300 g of expanded graphite as a conductive material, 50 g of polytetrafluoroethylene-hexafluoropropylene copolymer as a binder and 1 part of water.
kg was mixed in a Henschel mixer for 15 minutes. This was dried at 150 ° C. for 16 hours to obtain a positive electrode mixture. Each of these positive electrode mixes was adjusted to 450 mg to 1000
It was weighed by turning and slicing, and the variation in the weight was examined. Table 1 shows the results.

[0011]

[Table 1]

As is clear from Table 1, the positive electrode mixture of the example showed a small variation in measured value of about 1/3 as compared with the positive electrode mixture of the comparative example, and a uniform sized product was obtained. I understand. The positive electrode mixture obtained as described above was added to 2 to 4 t /
It was pressure-molded into a pellet at cm ² . 250 ° C
And dried with hot air to obtain positive electrode material mixture pellets.

Next, using the positive electrode mixture of each of the examples and comparative examples, as shown in FIG. 4, a diameter of 20 mm and a height of 1
A 6 mm coin type lithium battery was produced. Inside the stainless steel battery case 20 also serving as a positive electrode terminal, a positive electrode pellet 25 is disposed in close contact with the battery case 20. On the positive electrode pellet 25, a separator 24 made of polypropylene fiber non-woven fabric impregnated with a non-aqueous electrolyte solution is provided.
Is arranged. The opening of the battery case 20 is sealed by a stainless steel sealing plate 21 which also serves as a negative electrode terminal, and the negative electrode active material 22 made of lithium bonded to the inside of the sealing plate 21 is pressure bonded to the separator 24. .
A polypropylene gasket 23 having a surface coated with a sealing agent 26 is sandwiched between the battery case 20 and the sealing plate 21, and the open end of the battery case 20 is caulked inward to seal the battery.

The coin type batteries using the positive electrode mixture of the examples and the comparative examples were continuously discharged (high load discharge) at a temperature of 20 ° C. with a resistance of 1 kΩ as a load. The result is shown in FIG. At an ambient temperature of 20 ° C., 40
Discharge was performed for 15 seconds using a load of 0Ω as a load, and a voltage change (closed circuit voltage characteristic) due to the load was examined. FIG. 6 shows the result.

From FIG. 5, it is confirmed that the battery of Example has a higher battery voltage at the time of high load discharge and the discharge capacity is also improved as compared with the battery of Comparative Example. As shown in FIG. 6, the battery of the example has a smaller voltage drop than the battery of the comparative example even in the closed circuit voltage characteristic. It is considered that this is because the battery of the example has a large porosity of the positive electrode mixture, and thus the reaction of the active material inside the positive electrode is more likely to proceed than the battery of the comparative example which is a conventional product.

Desirable as a positive electrode mixture for batteries 4
In order to obtain a product having a particle size range of 0 to 500 μm with a high yield, it is necessary to set the diameter of the through hole of the die to 0.3 mm or less. However, in the conventional extrusion granulator, the die surface is flat, and the pressure applied to the die when the positive electrode mixture is extruded by the screw becomes uneven,
If the diameter of the through hole is small, the die is likely to generate heat or break. Therefore, the diameter of the through hole of the die could not be 0.5 mm or less, and the yield with the above particle size was low. According to the present invention, by using a hemispherical die, it becomes possible to easily use a die having a through hole with a diameter of 0.3 mm or less, which results in 40 to 50.
Granules in the particle size range of 0 μm can be obtained in high yield. Further, the positive electrode mixture produced by the production method of this example is softer than that obtained by granulation by a conventional stirring and mixing type granulator or the like, and a granulated product having a large porosity can be obtained. Therefore, it is possible to obtain a positive electrode mixture which is excellent in the liquid absorbing property of the electrolytic solution, and as a result is excellent in the discharge characteristics even under a heavy load.

In the above examples, the organic electrolyte battery using manganese dioxide as the main active material of the positive electrode mixture was used, but similarly, metal oxides such as copper oxide and silver chromate,
Alternatively, the same effect can be obtained when a carbon halide such as fluorocarbon is used as the main active material. Further, as a battery system, in addition to the organic electrolyte battery, this type of structure can be sufficiently applied to an alkaline battery and a Lucranche battery.

[0018]

EFFECTS OF THE INVENTION According to the present invention, it is possible to reduce the variation in weight in weighing the positive electrode mixture by slicing. Further, it is possible to provide a positive electrode mixture having high reaction efficiency and excellent discharge characteristics even under heavy load.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of a granulator used in an example of the present invention.

FIG. 2 is a vertical sectional view showing the structure of a particle size regulator used in an example of the present invention.

FIG. 3 is an enlarged view of a main part of the particle size regulator, where (a) is a vertical sectional view and (b) is a perspective view.

FIG. 4 is a vertical cross-sectional view of a coin-type lithium battery used for evaluation of a positive electrode mixture in an example of the present invention.

FIG. 5 is a characteristic diagram showing a continuous discharge curve of a coin-type lithium battery using the positive electrode mixture of the present invention.

FIG. 6 is a characteristic diagram showing a voltage change due to a load of the battery.

[Explanation of symbols]

 1 Semi-Circular Die 2 Extrusion Screw 3 Extrusion Blade 4 Mixture 5 Hopper 6 Cylinder 7 Through Hole 8 Cylindrical Granule 10 Hopper 11 Cylindrical Container 12 Rotating Disc 13 Rotating Shaft 14 Air Jet Hole 15 Air Chamber 16 Exhaust Damper 17 Granular product 20 Battery case 21 Sealing plate 22 Negative electrode active material 23 Gasket 24 Separator 25 Positive electrode pellet 26 Sealant

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumio Oo 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A screw in-line type in which a wet mixture containing a positive electrode active material, a binder and a conductive material is extruded into a cylinder equipped with a hemispherical die having a large number of circular through holes at its tip. In the granulator, the step of producing a granulated product of the mixture by extruding from the through hole by the rotation of the extrusion screw, the cylindrical container of the sealed type and the horizontally arranged in the cylindrical container, Using a granulator equipped with a rotating disc having a frame-shaped side wall protruding in the direction, the cylindrical container, and a mechanism for blowing air from a gap between the rotating disc, the granulated product is rotated on the rotating disc. The method for producing a positive electrode mixture for a battery, which comprises the step of molding into a spherical shape by charging the mixture into a positive electrode. 2. The diameter of the through hole of the hemispherical die is 0.
It is 3 mm or less, The manufacturing method of the positive electrode mixture for batteries of Claim 1. 3. The method for producing a positive electrode mixture for a battery according to claim 1, wherein the positive electrode active material is at least one selected from the group consisting of metal oxides, sulfides, halides and carbon halides.